RFID tag

ABSTRACT

The present invention provides an RFID tag excellent in the diffusion of heat. The RFID tag includes a base, an antenna pattern that is provided on the base and forms a communication antenna, a circuit chip that is electrically connected to the antenna pattern and performs radio communication via the antenna, a cover that is provided in close contact with the base in such a manner as to cover the antenna pattern except a prescribed region including the circuit chip, and an insulating thermal diffusion material that covers the prescribed region and is in thermal contact with the circuit chip. The insulating thermal diffusion material has thermal conductivity higher than the thermal conductivity of the cover.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation application of application Ser. No.11/085,491, filed Mar. 22, 2005, now U.S. Pat. No. 7,199,718 , theentire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an RFID (Radio FrequencyIdentification) tag that performs information exchange with externalequipment in a noncontact manner. Incidentally, among those skilled inthe art related to the technical field of the present application, the“RFID tag” used in the specification of the present application maysometimes be called an “inlay for RFID tag” by regarding the “RFID tag”as an internal component member (inlay) for “RFID tag.” Oralternatively, in some cases, this “RFID tag” may be referred to as “aradio IC tag.” Also, a noncontact type IC card is included in this “RFIDtag.”

2. Description of the Related Art

In recent years, there have been proposed various RFID tags that performinformation exchange with external equipment represented by areader/writer in a noncontact manner by use of radio waves. As one kindof this RFID tag, there has been proposed an RFID tag in which anantenna pattern for radio communication and an IC chip are mounted on abase sheet made of plastics or paper. A conceived mode of using an RFIDtag of this type is such that the RFID tag is stuck to an article andthe like and performs the identification of the article by exchanginginformation on the article with external equipment.

In such RFID tags, it has been proposed that a cover that covers a basesheet be provided in order to protect an antenna pattern or an IC chip.

FIGS. 1(A) and 1(B) are a front view and a side view, respectively, of aconventional RFID tag. The side view shown here is a drawing in whichthe internal structure is seen through from the side-surface side of theRFID tag. In this specification, drawings hereinafter called a side vieware all similar drawings.

An RFID tag 1 shown in FIGS. 1(A) and 1(B) is constituted by an antennapattern 3 provided on a base sheet 2, an IC chip 4 that is bonded to thebase sheet 2 with an epoxy adhesive 7 and electrically connected to theantenna pattern 3 via a bump 5, and a cover sheet 6 bonded to the basesheet 2 in such a manner as to cover the antenna pattern 3 and the ICchip 4. The cover sheet 6 is usually formed from a material selectedfrom among PET materials, polyester materials, polyolefin materials,polycarbonate materials, acrylic materials, etc.

This RFID tag 1 receives the energy of an electromagnetic field releasedby a reader/writer as electric energy by use of the antenna pattern 3and the IC chip 4 is driven by the electric energy, whereby thecommunication action is realized.

In the RFID tag 1 constructed as described above, the height of the ICchip 4 portion is larger than the height of other portions. Therefore,when something rubs the cover sheet 6 of the RFID tag 1 and when theRFID tag 1 is used in such a manner as to be sandwiched between books,impacts and loads are concentrated on the IC chip 4 and this might causetroubles in the IC chip 4 and faults such as the exfoliation of the ICchip 4. Furthermore, there is also a possibility that the stretch or sagof the cover sheet 6 occurs near the IC chip 4, generating residualstresses, with the result that the cover sheet 6 might come off due tothe residual stresses.

Compared to such RFID tags of typical structure, there have also beenproposed RFID tags in which ideas for protecting IC chips areincorporated (refer to, for example, U.S. Pat. No. 6,100,804, U.S. Pat.No. 6,265,977, U.S. Pat. No. 6,147,604, U.S. Pat. No. 6,215,401 and U.S.Pat. No. 6,294,998). In RFID tags disclosed in these patent documents,an IC chip is embedded in a sealing member or an intermediate layer andthe surface of the RFID tag is made flush, whereby the concentration ofimpacts and loads on the IC chip are avoided.

However, in such conventional RFID tags, the heat generated by the ICchip is captured and confined in due to the presence of the sealingmember and the intermediate layer and this might cause malfunctions ofthe IC chip. Also, in the case of the RFID tag 1 of a typicalconstruction as shown in FIGS. 1(A) and 1(B), the thermal conductivityof the cover sheet 6 is low, the thermal capacity of the IC chip 4itself is also low and, besides, also between the IC chip 4 and theantenna pattern 3, the greater part except the portion of the bump 5 isembedded with an epoxy adhesive 7 and the thermal resistance byconnection is large. For this reason, heat is apt to be captured andconfined in the IC chip 4. Therefore, in a case where the RFID tag 1 ispresent near a reader/writer and subjected to a strong electromagneticfield, it might be thought that the temperature rises abruptly due tothe heat generated in the IC chip 4. Such an abrupt temperature risemight cause malfunctions of the IC chip 4. Also, in a case where thetemperature of an article to which the IC chip 4 is stuck is constantlya high temperature of 50° C. to 70° C., even when the RFID tag 1 isplaced at a distance from a reader/writer, there is a possibility that acritical temperature for the stable operation in a transistor within theIC chip 4 and a critical temperature for long-term memory holding mightbe exceeded due to the heat generation from the IC chip 4.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesand provides an RFID tag excellent in the diffusion of heat.

An RFID tag of the present invention includes: a base; an antennapattern that is provided on the base and forms a communication antenna;a circuit chip that is electrically connected to the antenna pattern andperforms radio communication via the antenna; a cover that is providedin close contact with the base in such a manner as to cover the antennapattern except a prescribed region including the circuit chip; and aninsulating thermal diffusion material that covers the prescribed regionand is in thermal contact with the circuit chip, the insulating thermaldiffusion material having thermal conductivity higher than the thermalconductivity of the cover.

According to an RFID tag of the invention, because the thermal diffusionmaterial is provided, the RFID tag is excellent in the diffusion of heatand malfunctions by heat and the like are prevented. Also, because thecover does not cover the circuit chip, the coming off of the cover dueto residual stresses as described above is also prevented.

It is preferred that in the RFID tag, the thermal diffusion material beprovided with a center part on the circuit chip and a protective partthat encloses the center part, the height of the protective part beinglarger than the height of the center part.

By providing the thermal diffusion material having this protective part,the concentration of impacts and loads on the circuit chip can beavoided.

The thermal diffusion material in the RFID tag of the invention may beformed by bonding a sheet-like member to the prescribed region or may bea liquid material that is applied to the prescribed region and hassolidified.

Such a thermal diffusion material as described above can be providedonly in an accepted product after an operation test in the process ofmanufacturing RFID tags and it becomes easy to distinguish betweenaccepted products and rejected products. When a liquid material is used,the manufacturing process becomes simple and cost reduction is expected.

The thermal diffusion material in the RFID tag of the invention may bean insulating material into which a thermally conductive granule havingthermal conductivity higher than the thermal conductivity of theinsulating material is mixed or the thermal diffusion material may havea lamellar structure including a first layer and a second layer havingthermal conductivity higher than the thermal conductivity of the firstlayer.

The case of the thermal diffusion material into which the thermallyconductive granule is mixed, is excellent in that an RFID tag of highthermal conductivity can be easily obtained. The case of the thermaldiffusion material having the lamellar structure, is excellent in thatan RFID tag excellent in both strength and the diffusion of heat can beeasily obtained.

As described above, the RFID tag of the invention is excellent in thediffusion of heat and malfunctions of the circuit chip by heat and thelike can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail based on the following figures, wherein:

FIGS. 1(A) and 1(B) are a front view and a side view, respectively, of aconventional RFID tag;

FIGS. 2(A) and 2(B) are a front view and a side view, respectively, ofthe first embodiment of the present invention;

FIG. 3 is a conceptual diagram of the process of manufacturing an RFIDtag;

FIG. 4 is a detail drawing of the perforation step shown in FIG. 3;

FIGS. 5(A) and 5(B) are a front view and a side view, respectively, of asemifinished product;

FIGS. 6(A) and 6(B) are a front view and a side view, respectively, ofan intermediate product after the laminating step;

FIGS. 7(A) and 7(B) are each a detail drawing of a thermal diffusionmaterial;

FIG. 8 is an explanatory drawing of the thermal diffusion materialaddition step shown in FIG. 3;

FIG. 9 is a drawing that shows the second embodiment of the invention;

FIG. 10 is a drawing that shows another manufacturing method in thesecond embodiment of the invention;

FIG. 11 is a drawing that shows the third embodiment of the invention;

FIG. 12 is a drawing that shows the fourth embodiment of the invention;and

FIG. 13 is a drawing that shows the fifth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below byreferring to the drawings.

FIGS. 2(A) and 2(B) are a front view and a side view, respectively, ofthe first embodiment of the present invention.

An RFID tag 10 shown in FIGS. 2(A) and 2(B) is constituted by an antennapattern 12 provided on a base sheet 11, an IC chip 13 that is bonded tothe base sheet 11 with an epoxy adhesive 17 and electrically connectedto the antenna pattern 12 via a bump 16, a cover sheet 14 bonded to thebase sheet 11 in such a manner as to cover the antenna pattern 12 exceptan area near the IC chip 13, and a thermal diffusion material 15 bondedto the cover sheet 14 and the IC chip 13 from above the IC chip 13.

Also this RFID tag 10 receives the energy of an electromagnetic fieldreleased by a reader/writer as electric energy by use of the antennapattern 12 and the IC chip 13 is driven by the electric energy, wherebythe communication action is realized.

In this first embodiment, the base sheet 11 corresponds to an example ofthe base of the invention, the antenna pattern 12 corresponds to anexample of the antenna pattern of the invention, the IC chip 13corresponds to an example of the circuit chip of the invention, thecover sheet 14 corresponds to an example of the cover of the invention,and the thermal diffusion material 15 corresponds to an example of thethermal diffusion material of the invention.

Although the cover sheet 14 is formed from a PET material, the coversheet 14 may also be formed from a material selected from amongpolyester materials, polyolefin materials, polycarbonate materials,acrylic materials, etc. The bonding of the IC chip 13 is possible byusing an epoxy film in place of the epoxy adhesive 17.

Although details of the construction of the thermal diffusion material15 will be given layer, this thermal diffusion material 15 has thermalconductivity higher than the thermal conductivity of the cover sheet 14and holds the temperature of the IC chip 13 at low levels by efficientlydiffusing the heat generated by the IC chip 13 into the air and thelike, thereby making it possible to realize stable operation and thelike. Furthermore, because the structure in which this thermal diffusionmaterial 15 is bonded from above the IC chip 13 does not cause thestretch or sag of the cover sheet 15, there is no possibility that thethermal diffusion material 15 and the cover sheet 14 might come off dueto residual stresses.

The method of manufacturing the RFID tag 10 will be described below.

FIG. 3 is a conceptual diagram of the process of manufacturing an RFIDtag.

The RFID tag 10 shown in FIGS. 2(A) and 2(B) is manufactured from asemifinished product 21 of an RFID tag and a laminate film 22 byundergoing a perforation step 20, a laminating step 30, a test step 40and a thermal diffusion material addition step 50.

In the perforation step 20, holes are made in the laminate film 22 byuse of a perforating jig 23. In the laminating step 30, a sheet in whicha large number of semifinished products 21 are linked together and thelaminate film 22 are transferred by transfer rolls 31 and superposed oneach other, and the semifinished product 21 and the laminate film 22 arebonded together by being heated and pressurized by a thermocompressiondevice 32. In the test step 40, an operation test of an IC chip 13 in aregion enclosed with electromagnetic shields 42 by use of areader/writer 41 is performed to ascertain whether the product has acapacity necessary for an RFID tag. In the thermal diffusion materialaddition step 50, a silicone grease, which is a kind of thermallyconductive grease, is applied by use of a dispenser 51 and the thermaldiffusion material is stuck by use of a sticking jig 52.

FIG. 4 is a detail drawing of the perforation step 20 shown in FIG. 3.

In this perforation step 20, holes are made by the perforating jigs 23in places corresponding to the IC chip 13 of FIGS. 2(A) and 2(B) in thelaminate film 22 of a PET material that constitutes the cover sheet 14shown in FIGS. 2(A) and 2(B). The laminate film 22 in which holes havebeen made is transferred in the direction indicated by an arrow A in thefigure and superposed on a sheet in which a large number of semifinishedproducts 21 are linked together. And the laminate film 22 superposed onthe sheet containing the semifinished products 21 is delivered to thelaminating step 30 shown in FIG. 3.

FIGS. 5(A) and 5(B) are a front view and a side view, respectively, of asemifinished product.

In FIGS. 5(A) and 5(B), one of many semifinished products 21 that arelinked together in sheet form is illustrated, and in this semifinishedproduct 21, the antenna pattern 12 and the IC chip 13 are provided in anexposed condition on the base sheet 11. The method of manufacturing thissemifinished product 21 itself is the same as used in the manufacture ofconventional RFID tags and is not directly related to the presentinvention. Therefore, a description of the method of manufacturing thissemifinished product 21 is omitted here.

FIGS. 6(A) and 6(B) are a front view and a side view, respectively, ofan intermediate product after the laminating step.

Also in FIGS. 6(A) and 6(B), one of semifinished products 21 that areessentially linked together in a large quantity in sheet form isillustrated.

As shown in FIGS. 6(A) and 6(B), the cover sheet 14 is formed in thelaminating step and in this cover sheet 14 a hole 14 a is made in a partcorresponding to the IC chip 13.

This intermediate product is delivered to the test step 40 shown in FIG.3 to ascertain whether the intermediate product has a capacity necessaryfor functioning as an RFID tag. For a rejected product that has beenjudged to have an insufficient capacity in this test step 40, itsposition in the sheet in which many intermediate products are linkedtogether is recorded, and this rejected product is delivered as it is tothe thermal diffusion material addition step 50 shown in FIG. 3.

FIGS. 7(A) and 7(B) are each a detail drawing of a thermal diffusionmaterial.

Details of the lamellar structure of the thermal diffusion material 15are shown in FIG. 7(A). The thermal diffusion material 15 has a lamellarstructure constituted by an insulating silicone rubber sheet 15 a, anelectrically conductive graphite sheet 15 b and an insulating, stickypolyimide tape 15 c. For the thickness of each layer, thicknesses of 20μm to 100 μm are suitable for the silicone rubber sheet 15 a,thicknesses of 10 μm to 100 μm are suitable for the graphite sheet 15 b,and thicknesses of 20 μm to 50 μm are suitable for the polyimide tape 15c. The silicone rubber sheet 15 a has strength higher than the strengthof the graphite sheet 15 b, while the graphite sheet 15 b has thermalconductivity higher than the thermal conductivity of the silicone rubbersheet 15 a. For this reason, the thermal diffusion material 15 is toughand excellent in thermal diffusion. The silicone rubber sheet 15 acorresponds to an example of the first layer of the invention, and thegraphite sheet 15 b corresponds to an example of the second layer of theinvention. The polyimide tape 15 c is a kind of sticky material and thethermal diffusion material 15 is bonded to the intermediate product withthe polyimide tape 15 c.

As shown in FIG. 7(B), this thermal diffusion material 15 as describedabove is obtained by punching a sheet 18 and shaped like a patch, andthis patch-like thermal diffusion material 15 is stuck in the thermaldiffusion material addition step in such a manner as to block the hole14 a of the intermediate product shown in FIGS. 6(A) and 6(B).

FIG. 8 is an explanatory drawing of the thermal diffusion materialaddition step 50 shown in FIG. 3. In this figure, however, only part ofthe step at which the thermal diffusion material is stuck by use of thesticking jig is shown.

For an intermediate product that has been accepted in the operation testin the test step, a silicone grease 19 to improve adhesion to thethermal diffusion material 15 is applied to the IC chip 13 by use of thedispenser 51 shown in FIG. 3, and the thermal diffusion material 15 isstuck on the silicone grease 19 by use of the stacking jig 52. On theother hand, for an intermediate product that has been rejected in theoperation test and its position has been recorded as a rejected product,neither the application of the silicone grease 19 nor the sticking ofthe thermal diffusion material 15 is performed, and this rejectedproduct is left as an intermediate product. As a result of this,accepted products can be distinguished at a glance from rejectedproducts and the mixing of rejected products is prevented. Incidentally,although wax-based phase-changing materials that liquefy by theapplication of heat can be adopted in place of thermally conductivegreases represented by this silicone grease 19, in this embodiment thesilicone grease 19 is to be used.

The sticking jig 52 has a center projection 52 a that pushes a centerpart 15 e of the thermal diffusion material 15 against the IC chip 13,and a ring 52 b that pushes an edge part 15 d of the thermal diffusionmaterial 15 against the cover sheet 14, and the height of the centerprojection 52 a is larger than the height of the ring 52 b. For thisreason, the height of the edge part 15 d of the thermal diffusionmaterial 15 bonded to the cover sheet 14 by the ring 52 b is larger thanthe height of the center part 15 e of the thermal diffusion material 15pushed against the IC chip 13 by the center projection 52 a. This centerpart 15 e corresponds to an example of the center part of the inventionand the edge part 15 d corresponds to an example of the protective partof the invention.

Because the height of the edge part 15 d is larger than the height ofthe center part 15 e in this manner, impacts and loads on the RFID tagare applied to the edge part 15 d and impacts and loads on the centerpart 15 e and the IC chip 13 are relieved, with the result that thebreakage and exfoliation of the IC chip 13 are prevented.

With this the description of the first embodiment of the presentinvention is finished, and other embodiments of the invention will bedescribed below. Incidentally, each of the embodiments described belowis the same as the first embodiment described above, with the exceptionthat different thermal diffusion materials are used. Therefore, thefollowing descriptions will be given by paying attention to onlydifferences from the first embodiment and overlaps in descriptions willbe avoided.

FIG. 9 is a drawing that shows the second embodiment of the invention.

An RFID tag 60 of the second embodiment shown in FIG. 9 is provided witha thermal diffusion material 61 formed from a ceramic (Al₂O₃: alumina,SiO₂: silica) powder. This thermal diffusion material 61 is formed byblowing a liquid ceramic paint (for example, the ceramic α made by OkiElectric Industry Co., Ltd.) from a nozzle 54 through an opening of amask 55 and causing the liquid ceramic paint to solidify by drying orthe like.

FIG. 10 is a drawing that shows another manufacturing method in thesecond embodiment of the invention.

A thermal diffusion material 61 in the RFID tag 60 of the secondembodiment can also be formed by applying the above-described liquidceramic paint by use of a dispenser 56 and causing the liquid ceramicpaint to solidify by drying or the like.

Thus, in the RFID tag 60 of the second embodiment the manufacture of thethermal diffusion material 61 is easy and cost reduction is expected.

FIG. 11 is a drawing that shows the third embodiment of the invention.

An RFID tag 70 of the third embodiment is provided with a thermaldiffusion material 71 formed from a silicone rubber sheet and thisthermal diffusion material 71 is bonded directly to the IC chip 13.Because this thermal diffusion material 71 has a very simpleconstruction, its manufacturing cost is thought to be held down.Incidentally, although it might be thought that the capacity for thermaldiffusion in the third embodiment is inferior to the capacity forthermal diffusion in the first embodiment mentioned above, it isexpected that the third embodiment is superior to conventionaltechniques and, therefore, sufficient usability is expected under someservice conditions.

FIG. 12 is a drawing that shows the fourth embodiment of the invention.

An RFID tag 80 of the fourth embodiment is also provided with the samethermal diffusion material 71 formed from a silicone rubber sheet aswith the RFID tag of the third embodiment and the area around the ICchip 13 is embedded with a silicone grease 81 to improve thermaldiffusion properties. In this RFID tag 80, both cost reduction and animprovement in thermal diffusion properties are achieved and itsapplications are thought to be wide.

FIG. 13 is a drawing that shows the fifth embodiment of the invention.

An RFID tag 90 of the fifth embodiment is provided with a thermaldiffusion material 91 that is formed by mixing a ceramic (Al₂O₃:alumina, SiO₂: silica) granule 92 of high thermal conductivity into aninsulating silicone sheet. As with the thermal diffusion material 15 inthe first embodiment, this thermal diffusion material 91 is bonded withan adhesive.

Because in this thermal diffusion material 91, thermal conductivity canbe easily adjusted by adjusting the kind and mixed amount of granule 92,the thermal diffusion material 91 of high thermal conductivity can beeasily obtained.

Although in the above description, a cover sheet in which holes are madebeforehand in the perforation step is shown as an example of the coverof the present invention, the cover of the invention may be such thatthe cover once covers the whole base and after that, part of the coverin an area near the circuit chip is stripped off.

Also, in the above description, the base sheet or the cover sheet isshown as an example of the base or cover of the invention. However, theshape of the base or cover of the invention is not limited to the sheet.

Also, in the above description, a protective part obtained by sticking athermal diffusion material is shown as an example of the protective partof the invention. However, the protective part of the invention may be apart shaped like a projection formed in the thermal diffusion materialbefore affixing the thermal diffusion material to the circuit chip.

1. A method of manufacturing an RFID tag, comprising: providing a coverin close contact with a base in such a manner as to cover an antennapattern except a chip-mounted region where a circuit chip is mounted onthe base, the circuit chip electrically-connected to the antennapattern, the antenna pattern provided on the base; providing a thermaldiffusion material in thermal contact with the circuit chip by coveringa prescribed region with the thermal diffusion material, wherein thethermal diffusion material has a thermal conductivity higher than thecover; and testing an operation of the circuit chip after said providingthe cover in close contact with the base, wherein the thermal diffusionmaterial is bonded on the circuit chip when the circuit chip has passedthe operation test.
 2. The method of manufacturing an RFID tag accordingto claim 1, wherein said providing the cover in close contact with thebase includes perforating a hole on a laminate film forming the cover;and laminating the laminate film on the base while positioning the holeat the chip-mounted region.
 3. The method of manufacturing an RFID tagaccording to claim 1, wherein the operation test of the circuit chip isperformed in a region enclosed with electromagnetic shields.
 4. Themethod of manufacturing an RFID tag according to claim 1, wherein thethermal diffusion material is bonded on the circuit chip via siliconegrease.
 5. The method of manufacturing an RFID tag according to claim 1,wherein the thermal diffusion material is an electrically-insulatingthermal diffusion material.